In general, in a substrate processing apparatus for performing a processing on a semiconductor wafer (hereinafter, referred to as “wafer”) as a substrate, there are generated particles, e.g., fine fragments of aluminum, caused by a contact between the wafer and a mounting table for mounting thereon the wafer, reaction products, e.g., fluorocarbon-based polymer, caused by a reaction of a processing gas or the like. Such particles are adhered to the wafer and thus deteriorate quality of a semiconductor device formed on a surface of the wafer.
As for a method for removing particles adhered to a wafer, there has been known a wet cleaning method for cleaning a dry-etched wafer in a fluoric acid solution or pure water in a wet processing chamber. In accordance with such method, the particles adhered to the wafer can be removed during a dry etching process (see, e.g., U.S. Pat. No. 5,135,608).
However, in the aforementioned wet cleaning method, pure water or the like is ejected mostly toward a surface of the wafer. Therefore, particles adhered to a backside of the wafer, i.e., foreign substances adhered to an entire backside of the wafer or bevel polymer adhered to a peripheral portion of the backside of the wafer, cannot be removed.
The wafer is kept afloat by the particles adhered to the backside of the wafer while it is mounted on the mounting table, so that, during a lithography process for exposing a photoresist coated on the wafer surface, a distance between the wafer and an exposure device does not coincide with a focal length of the exposure device and, therefore, a mask pattern cannot be precisely reproduced on the wafer surface. Consequently, the quality of a semiconductor device formed on the corresponding wafer is deteriorated.
In case wafers undergone a predetermined plasma process are transferred in an airtight container such as a FOUP for holding a plurality of wafers in parallel, particles detached from a backside of a wafer held in an upper level in the FOUP may fall downward to be adhered to a surface of a wafer held in a lower level in the FOUP, thereby deteriorating the quality of a semiconductor device formed on the wafer held in the lower level in the FOUP.
In the aforementioned wet cleaning method, a flow of the pure water used for a wet cleaning is not controlled. Thus, even if the particles and/or the bevel polymer are removed from the backside of the wafer, they can be adhered again to a surface of a wafer which is undergoing a predetermined process, e.g., a drying treatment, at a vicinity of a wet cleaned wafer. Consequently, the quality of a semiconductor device formed on the wafer can be deteriorated.